docs: def add_completion(self, text, name, field, size=None, params=None):
          """
          Add completion-type suggestion:
  
          http://www.elasticsearch.org/guide/en/elasticsearch/reference/current/search-suggesters-completion.html
  
          :param text: text for searching using autocompletion
          :param name: name for the suggester
          :param field: document's field to be autocompleted
          :param size: (optional) size of the autocomplete list
          :return:
          """
          data = {
              'field': field
          }
  
          if size:
              data['size'] = size
  
          if params:
              data.update(params)
  
          self.fields[name] = {
              'text': text,
              'completion': data,
          }